Process for producing 7-dehydrosterols



Patented Mar. 27,1951

PRGCESS FOR PRODUCING 7 -DEHYDROSTEROLS William L. Ruigh, Summit, N. J., and David H. Gould, Hickory Hiil, N. Y., assignors to Nopco Chemical Company, Harrison, N. 5., a corporation of New Jersey No Drawing. Application May 14, 1949, Serial No. 93,408

9 Claims.

genation process and more particularly to a highly improved process for producing 7-dehydrosterols.

Since the discovery of Ziegler (Annalen 551, 80419) that the halogenation of organic compounds at a carbon atom alpha to a double bond could be accomplished by using compounds such as N-halogenated acid amides and imides as halogenatingagents, a great deal of research has been carried out on the application of this reaction to the production of 'Z-clehydro derivatives of various sterol compounds. The greater part of this work has been directed to the production of 'Z-dehydrocholesterol. As is well known, 'Z-tiQhY- .drocholesterol is readily converted to vitamin D3 by irriadiation with ultra-violet light. In order to form 7-dehydrocholesterol from the halogencholesterol compounds produced in accordwith the Ziegler process, it is necessary to subject the halogenated sterol compounds to dehydrohalog'en-ation with a suitable dehydrohalogenat ing agent. The compounds which have been most frequently employed to react with the halogenated sterol derivatives to effect dehydrohalogenation are compounds such as dimethylaniline,

diethylaniline, collidine, and quinoline. Conrpounds such as triethyl amine, DLN-dipropylaniline, l T-ethy1-piperidine and N ,N-diethylcy olohexyl amine have also been employed for this purpose. Of these. many prior art dchydro= halogenating agents, it. has been our experience that diethylaniline has been by far the most satisfactory and has given the highest yields and the highest purity as compared to. any of the other compounds above mentioned.v Patent No. 574,432, the results which are set forth therein appear to indicate the same result, 1.. e. that diethylaniline is by far the most satisfactory dehydrohalogenating agent so far known. Although diethylanil'ine has proved to be fairly successful as a dehydrohalogenating agent, the yields of 'Y-dehydro compounds which are ob tained even when it is employed as the dehydrohalogenating agent are not as high as desired. Furthermore, the purity of the products which are obtained in accordance with the prior'art "methods is often not as high as desired.

It is the object of this invention to provide a new and highly improved process for producing 7-dehydrosterols.

A further object of the invention is to. provide a new and highly improved process for dehydrohalogenating halogenated sterol compounds which will give much higher yields than the prior art methods for dehydrohalogenation and, which In British 2 higher yields will be of productshaving a purity higher than the products obtained by the prior art dehydrohalogenation processes.

.Other objects of the invention will in part be obvious and will in part appear hereinafter.

We have discovered that the above and other objects of the invention may be realized if the dehydrohalogenation of a halogenated sterol compound is effected by reacting the halogenated sterol compound with quinaldine. The yields of the desired 7-dehydrosterol compounds which are obtained are substantially higher when the dehydrohalogenation is effected in this manner than when the dehydrohalogenation is carried out in accordance with the disclosures of the prior art. Furthermore, the products which are obtained in these substantially higher yields are generally of considerably higher purity than the products which are obtained when the dehydrohalogenation is carried out in accordance with the methods of the priorart.

As we have stated above, it is possible to obtain considerably higher yields of the desired 7-dehydrosterol compound by effecting the dehydrohalogenation of the halogenated sterol compound by merely reacting the desired halogenated sterol compound with quinaldine. The yields obtained in this manner are often higher by as much as 50% or more than the yields obtained when the dehydrohalogenation is carried out in accordance with the prior art methods using one of the dehydroh-alogenating agents referredto above.

The amount of quinaldine which is employed in the reaction should be sufficient, of course, to react completely with the halogenated sterol compound which is to be dehydrohalogenated, i. e. at least a mole to mole ratio should be employed. As a matter of convenience, it is usually preferred to use an excess of quinaldine over the amount theoretically required to bring about the dehydrohalogenation reaction. Thus from about three moles toabout six moles of quinaldine per mole of halogenated sterol compound are coneniently employed, Larger amounts of quinaldine per mole of halogenated sterol compound may be employed, if desired,,but the use of such larger amounts is not necessary. In order to obtain the most consistent results, it is preferred that quinaldine in a fairly high state of purity be used. Commercial quinaldine can be purified by fractional distillation or quinaldine can be synthesized by a modified Skraup synthesis In both cases the quinaldine is of a suitable purity and will consistently give excellent results when droxyl group at the 3 position.

employed to bring about the dehydrohalogenation of a halogenated sterol compound. if desired, however, quinaldine containing appreciable amounts of impurities can be employed successfully in the process of the invention.

In carrying out the process or the invention, it is necessary to heat the mixture of quinaldine and halogenated sterol compound in order to bring about the dehydrohalogenation reaction. In most cases, it is preferred to heat the reaction mixture to a temperature of about 90 C. to 100 (3., e. g. on a steambath. The reaction can be carried out, however, at a temperature between about 80 C. and about 150 C. and temperatures higher than 150 C. can be employed if desired, although such higher temperatures are not required. The length of time of heating the reaction mixture will vary slightly depending upon the temperature at which the reaction is carried out. is prefer to heat for about three hours when a temperature of about 90 C. is maintained. At higher temperatures,shorter periods of heating may be employed.

After the dehydrohalogenation reaction has been accomplished, the desired 7-dehydrosterol may be recovered from the dehydrohalogenation reaction mixture in any convenient manner. The exact method employed for isolating the T-dehydrosterol compound will depend to some extent upon the specific derivative of the sterol employed as the starting material in the process.

It is quite well known that a sterol compound prior to being subjected to halogenation in accordance with the Ziegler process must be treated in some manner or other so as to convert the hydroxyl group on the 3 position to a group which will not be detrimentally affected by the halogenating agent but which can conveniently be reconverted to a hydroxyl group. Thus the hydroxyl group may be converted to an ester group or to an ether group or it may be replaced with any other suitable inactive group which may later be split off with re-formation oi the hy- The most com mon practice in the prior art and what appears to be the most suitable and most feasible practice is to convert the hydroxyl group to an ester group by esterification with an efiicient csterifying agent such as acetic anhydride, benzoyl chloride, or the like. If the sterol compound has been converted to an ester thereof, the sterol is re-formed by a simple hydrolysis of the ester group by saponification with alcoholic alkali. The practice in the prior art as shown by the British patent referred to hereinabove and by U. S. Patent No. 2,441,09l and its French counterpart, French Patent No. 901,551, has been to remove the dehydrohalogenating agent from the reaction mixture prior to carrying out the saponification' of the ester of the sterol compound. This is accomplished according to these prior art patents either by a process involving admixing the reaction mixture with an excess of an aqueous acid solution and extracting this mixture with a solvent such as other or a hydrocarbon solvent to remove the l-dehydrosterol ester from the aqueous" mixture, or it is accomplished by a process involving the admixing of the dehydrohalogenation reaction mixture with an excess of a water-immiscible solvent such as petroleum ether and then extracting that mixture with an aqueous acid solution to remove the dehydrohalogenating agent from the solvent solution. In either case the solvent solution containing the 7- dehydrosterol ester is then washed with a dilute esters.

alkali solution to remove any acid dissolved in thesolvent and thereafter the solvent solution is washed with water to remove any alkali dissolved in the solvent. Thereafter, the solvent is generally evaporated to recover the 7-dehydrosterol ester since the solvent which has been used in separating the ester from the dehydrohalogenation reaction mixture is generally a solvent Qtion reaction. In commercial practice, however, it is preferable to carry out the saponification of the esters in accordance with the new and highly improved process which is disclosed and "claimed in U. S. Patent Application Serial No. 781,497 filed by K. H. Schaaf on October 22, 1947.

..he details of this process are set forth herein in Example III and Example IV. This process eliminates entirely the separation of the 'Y-dehydrosterol ester from the dehydrohalogenating agent prior to eifecting the saponification of the ester. Instead the saponification is carried out directly in the reaction mixture obtained from the dehydrohalogenation reaction by dissolving the dehydrohalogenation reaction mixture in an excess of an alcoholic alkali solution wherein the alcohol is one containing not more than 4 car- 'bon atoms, saponifying the 7-dehydrosterol ester in the resulting mixture, and cooling the solution to a temperature somewhat below room tempera-- ture whereupon the free 'Z-dehydrosterol crystal.- lizes from the solution in a relatively high state of purity. Any other suitable means of carrying out the saponification of Z-dehyolrosterol esters can, of course, be employed.

As mentioned above, it is common practice to block the hydroxyl group on the 3 position of the sterol compounds during the halogenation reaction by converting the hydroxyl group to a group which will not react with the dehydrohalogenating agent but which may later be reconverted to the hydroxyl group. For convenience, the term inactive group will be used herein in referring to such a group. For the purposes of the present invention, it is, of course, entirely immaterial just what inactive group is used to protect the 3 position of the sterol compound since the reaction between the halogenated sterol compound and the quinaldine involves, of course, the removal of the halogen atom from the 7 position on the sterol compound and the removal of the hydrogen atom from the 8 position of the sterol compound.

The specific examples given hereinafter show the use of the halogenated acetate and benzoate esters of chloresterol in the process of the invention. These examples are only illustrative and the reaction which takes place between these halogenated esters and quinaldine takes place with equal eiiiciency and ease between quinaldine and any other sterol compound having a double bond between the 5 and 6 carbon atoms and a halogen atom on the 7 carbon atom. Thus the 2 process of our invention is quite suitable for and is very effective in dehydrohalogenating any sterol compounds of this nature regardless "of whether they are the esters, the ethers or any other suitable derivatives of the particular sterol compound being dehydrohalogenated. Furthermore, as far as, the esters are concerned, any of the various sterol esters which may be formed can be dehydrohalogenated by the process of our invention. Among the ster-ol esters'which have been utilized in the prior art patents and which are quite suitable for use in the process of our invention, there may be mentioned the formats, the oxalate, the propionate, the butyrate, and the stearate esters of the halogenated sterol compounds as well as the acetate and benzoate esters thereof.

For a fuller understanding of the nature and objects of the invention, reference may be had to the following examples which are given merely as further illustrations of the invention and are not to be construed in a limiting sense:

Example I A mixture 0310.0 gms. of crude "Fbromocholesteryl benzoate and 15 mls. of relatively pure quinaldine was heated on a steam bath for 3 hours with stirring in the presence of .a nitrogen atmosphere. The reaction mixture was cooled, taken up in "75 mls. of 5% hydrochloric acid and extracted twice with 50 ml. portions of benzene. The benzene extracts were washed to neutralit with three 25 m1. portions of water. To the benzene solution there was added .a solution of 2.0 gms. of 85% KOH pellets in 40 mls. of ethanol. The mixture was refluxed for 1 hour in the presence of nitrogen to hydrolyze the "7- dehydrocholesteryl benzoate to 7-dehydr'ocholesterol. The cooled reaction mixture was poured into 15% mils. of water and the resulting mixture was extracted with four 50 ml. portions of ether. The ether extracts were washed with three .50 m1. portions of a 10% salt solution, then dried over sodium sulphate a .d thereafter the solvent was removed in vacuo. 6.16 sins. of a tan solid were obtained. A spectroscopic analysis of this material showed that the product had a purity of 41.5%, thus giving a yield of 7-dehydrochloresterol based on the amount of crude 7- bromocholesteryl benzoate employed of 37.8%.

Example II Another experiment was carried out in the same manner as that of Example I with the exception that diethylaniline (one of the prior art dehydro-halogenating agents) was employed in place of uinaldine. The crude 7-bromocholesteryl benzoate which was used was exactly the'same as that employed in Example I since it was merely another sample of material taken from the same batch of material from which the crude 7-bromochlolesterol benzoate used in Example I was obtained. A light tan solid weighing 7.05 gms. was obtained. Spectroscopic analysis of this product showed that it had a purity of only 26.2%, thus giving a yield of only 27.4% of the desired 7-dehydrosterol. Thus it is seen that based upon the purity of the product of this example the purity of the product obtained with quinaldine was about 66% greater than the purity of the product obtained with diethylaniline. Furthermore the yield obtained with quinaldine was nearl 40% greater than the yield obtained with diethylaniline.

Ezfiamplellll To a boiling hot solution or and) grams oi re crystallized cholesteryl acetate in 8 liters of; 311ml?" drous hexane there were added 9.3.41 grams ct lauroyl peroxide and 1046 grams of powdered, crude 6.05% N-bromosuccinimidel, The mix.- ture was heated to boiling and then allowed to react for a period of 13 minutes after which the reaction mixture was cooled to about 55 and filtered with suction. The succinimid'e which was filtered off was washed twice with 500 ml. portions of hexane. The filtrate and washings were combined and 3 liters of dried diethylaniline (one of the prior art dehydrohalogenating agents) added thereto, yielding a mixtur weighing 10,821 grams.

971 grams of the mixture were heated in a water bath in vacuo (N2 atm.) to distill ,ofi, the hexane. The residual diethylaniline solution thus obtained was heated at 98 C.-.9.l C. at 40 mm. pressure for .3 hours with stirring (1N2 atm. l. To the reaction mixture there was then added a hot solution of 79.4 grams of 87% KQH pellets in 825 ml. of ethanol and the mixture refluxed-in a water bath for one-half hour with stirring (N2 atm.). The reaction mixture was then chilled to +4 C. withstirring to crystallize theY'Z-dehydro cholesterol. Then 120 ml. of water were slowly added and the mixture stored at +2 C. overnight.

The solids were filtered off at room temperature and washed first with four 150 portions .of water and then with two 100 ml. portions of ice-cold 85% ethanol. The crude. crystalline "7-deh-ydrochclesterol was dried at F. in a vacuum drier and yielded 99.9 grams ota dark-- cream, crystalline solid. Froma spectroscopic analysis the following results were obtained:

54..4% purity 30.25% overall yield from cholesteryl acetate Example IV To a boiling hot solution of 200.0 grams of recrystallized .cholesteryl acetate in 850 ml. of an,- hydrous hexane were added 102.9 grams of powdered, recrystallized 97.4% .N-hromo'snc unnide and 9.939 gram ref lauroyl peroxide. This experi' ment was then conducted in essentially the same manner as that of Example III except. that stead of reacting diethylaniline with the halogenated sterol derivative, soc ml. of quhialdine were reacted with the halogenated sterol derivative.

.The crude 7-dehydrocholesterol, which was iso lated in the same manner as in Example III", amounted to 146.9 grams of a light-tan solid-. A spectroscopic analysis of this product gave the following results: 54.1% purity 44.2% overall yield from cholesteryl acetate.

The process of halogenating a sterol derivative with a compound such as N-bromosuccinimide in the presence of an organic peroxide, which proc ess was employed in Examples III and IV to prepare the halogenated sterol derivatives, is disclosed and claimed in copending U. S Patent Application Serial No. 765,631 of William L. Ruigh filed on August 1, 1947.

From the illustrative examples and the gen-- eral description of the invention given hereinabove, it is quite apparent that thefprocess of 7 our invention gives far greater yields of the de sired 7-dehydrosterols than can bec-btained when operating in accordance with the prior art methods. Furthermore the products which are obtamed by the process of our invention generally have a much greater purity than the products obtained by the prior art methods. Although the detailed examples given hereinabove have dealt with the treatment of esters of cholesterol, the process of our invention can be applied to the treatment of any esters of any similar sterol or to any other sterol derivative in which the 3 position is protected by some inactive group on the 3 position other than an ester group such as, for example, an ether group. The particular inactive group which is at the 3 position to protect that position from attack throughout the process of converting the sterol to a 'Z-dehydrosterol is entirely unimportant as far as the process of our invention is concerned inasmuch-as the parderivative having a double bond between the and 6 carbon atoms and having a halogen atom on the? carbon atom. 4

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

1. In a process for producing a 'l-dehydrosterol, the step which comprises reacting quinaldine with a sterol derivative selected from the group consisting of sterol esters and sterol ethers which have a double bond between the 5 carbon atom and the 6 carbon atom and which has a halogen atom attached to the 7 carbon atom, the reaction being carried out by heating the quinaldine and the halogenated sterol compound in contact with each other at a temperature of at least about 2. In a process for producing a 7-dehydrosterol,

the step which comprises reacting quinaldine with a cholesterol ether which has a double bond between the 5 carbon atom and the 6 carbon atom and which has a halogen atom attached to the '7 carbon atom, the reaction being carried out by heating the quinaldine and the halogenated sterol compound in contact with each other at a temperature of at least about 80 C.

' 3. In a process for producing a 7-dehydrosterol, the step which comprises reacting quinaldine with a sterol ester which has a double bond between the 5 carbon atom and the 6 carbonatom and which has a halogen atom attached to the 7 carbon atom, the reaction being carried out by heating the quinaldine and the halogenated sterol compound in contact with each other at a temperature of at least about 80 C.

- 4. In a process for producing a 7-dehydrostero1, the step which comprises reacting quinaldine with an ester of cholesterol which has a double bond between the 5 carbon atom and the 6 carbon atom and which has a halogen atom attached to the 7 carbon atom, the reaction being carried out by heating the quinaldine and the halogenated sterol compound in contact with each other at a temperature of at least about C.

\ 5. In a process for producing a 7 -dehydrostero1, the step which comprises reacting quinaldine with a benzoate ester of cholesterol which has a double bond between the 5 carbon atom and the 6 carbon atom and which has a halogen atom attached to the '7 carbon atom, the reaction being carried out by heating the quinaldine and the halogenated sterol compound in contact with each other at a temperature of at least about 80 C.

6. In a process for producing a 'Y-dehydrosterol, the. step which comprises reacting quinaldine with an acetate ester of cholesterol which has a double bond between the 5 carbon atom and the 6 carbon atom and which has a halogen atom attached to the '7 carbon atom, the reaction being carried out by heating the quinaldine and the halogenated sterol compound in contact with each other at a temperature of at least about 80 C.

7. In a process for producing a 7-dehydrosterol, the step which comprises reacting quinaldine with 7-bromocholesteryl benzoate, the reaction being carried out by heating the quinaldine and the halogenated sterol compound in contact with each other at a temperature of at least about 80 C.

8. In aprocess for producing a '7-dehydrosterol, the step which comprises reacting quinaldine with 7 -bromocholesteryl acetate, the reaction being carried out by heating the quinaldine and the halogenated sterol compound in contact With eachother at a temperature of at least about 80 C.

9. In a process for producing a 7-dehydrostero1, the step which comprises reacting quinaldine with 7-bromocholesteryl propionate, the reaction being carried out by heating the quinaldine and the halogenated sterol compound in contact with each other at a temperature of at least about 80 0.

'WILLIAM L. RUIGH.

DAVID H. GOULD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,023,075 Harris Dec. 3, 1935 2,255,815 Rosenberg Sept. 16, 1941 2,441,091 Van der Vliet et al. May 4, 1948 2,441,560 Butenandt May 18, 1948 2,476,424 Lowenbein July 19, 1948 

1. IN A PROCESS FOR PRODUCING A 7-DEHYDROSTEROL, THE STEP WHICH COMPRISES REACTING QUINALDINE WITH A STEROL DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF STEROL ESTERS AND STEROL ETHERS WHICH HAVE A DOUBLE BOND BETWEEN THE 5 CARBON ATOMS AND THE 6 CARBON ATOMS AND WHICH HAS A HALOGEN ATOM ATTACHED TO THE 7 CARBON ATOM, THE REACTION BEING CARRIED OUT BY HEATING THE QUINALDINE AND THE HALOGENATED STEROL COMPOUND IN CONTACT WITH EACH OTHER AT A TEMPERATURE OF AT LEAST ABOUT 80* C. 